More Pressure Venting Improvements to Be Required for Some Nuclear Plants

A new NRC memorandum to its technical staff calls for enhancing a March 2012 order requiring hardened venting systems at 31 boiling water reactors with Mark I and Mark II containments, considered more vulnerable to a Fukushima Daiichi-type accident.

The Nuclear Regulatory Commission is continuing to work on improving pressure venting systems in place at 31 boiling water reactors, in order to prevent explosions such as happened during the Fukushima Daiichi nuclear power plant's crisis in Japan. The NRC commissioners have directed technical staffers to follow a two-track approach, according to an agency news release.

A memorandum to the staff calls for enhancing a March 2012 order requiring hardened venting systems at 31 boiling water reactors with Mark I and Mark II containments. The memorandum starts rulemaking activities to produce requirements for these reactors to cool core debris and retain radioactive material in conjunction with venting during severe accidents. (A July 2012 report prepared for the NRDC that is available on the NRC's website explains that Mark I boiling water reactors' primary containments are only one-eighth the size of pressurized water reactors' containment and Mark IIs' are only one-sixth as large, and an NRC task force concluded the Mark Is have "a relatively high containment failure probability" for this reason.)

"In reaching this decision, the commission engaged in thoughtful deliberation with each other as we each considered these important issues in our post-Fukushima accident review process," said NRC Chairman Allison Macfarlane. "I compliment my colleagues and the staff for their sustained efforts on this issue and for taking a hard look at a complex matter."

Staffers now have 60 days to finalize the latest order, which will require the vents to handle the elevated pressures, temperatures, and radiation levels from a damaged reactor. It also will ensure nuclear power plant personnel can operate the vents safely under these conditions.

The news release says the commission has "given the staff a year to produce a technical evaluation to support rulemaking on filtering. During that time the staff will gather more public input as it completes its analysis. The Commission directed the staff to consider both the use of a filter to be placed on the vent, as well as a more performance-based approach using existing systems to achieve a similar reduction in radioactive release during an accident. The staff then must develop a draft rule and final rule, all by March 2017."

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